This disclosure relates to a pig for use to clean the interior wall of a pipeline. The interior surfaces of pipelines employed for moving fluids, whether liquids or gases, tend to become encrusted caused either by oxidation, or other chemical reaction, if the pipeline is made of metal, or deposits of solids from the fluid passing through a pipeline. Solids can be deposited on the interior of the pipeline whether it is made of metal or plastic. As solids adhere to the interior wall of the pipeline, or encrustation build up, the maximum fluid carrying potential of the pipeline is decreased. It has long been a practice of pipeline operators to periodically clean the interior of the pipelines by passing cleaning pigs through them.
A cleaning pig is a device that fits in the interior of a pipeline and is moved by fluid flow through the pipeline. Some means is provided on the pig to engage the interior wall of the pipeline to scrape or brush the interior to dislodge solid materials. For information relating to the use of pipeline pigs that have means for brushing or scraping the interior wall of a pipeline as it passes therethrough, reference may be had to the following U.S. Pat. Nos. 3,204,274; 3,879,790; 3,538,531; 3,605,159; 3,389,417; 3,474,479; 4,122,575; and 4,720,884.
One type of cleaning pig that has been successful is referred to in the trade as a "foam pig". Foam pigs are given this name since they are characteristically made out of plastic foam, such as polyurethane foam. This product has desirable characteristics when used to form a pipeline pig. It is semi-rigid, that is, it has strength and toughness and yet can be deformed. A foam pig can be made to have an external diameter slightly greater than the internal diameter of the pipeline in which the pig is to be used so that the pig is slightly compressed when it is inserted into the pipeline so as to securely urge the external surface of the pig against the pipeline interior wall.
Another reason for using polyurethane foam for making pigs is that it is durable and relatively inexpensive compared to making pigs having metal bodies or bodies made of rigid, non-flexible plastic.
To make a "foam pig", that is, a pig having a body made of polyurethane, function as a cleaning pig, it is usually desirable to increase the abrasiveness of the surface of the pig. One way of doing this is to attach a brushing element. This can be done by forming spiral grooves in the exterior surface of the foam pig and securing in the spiral grooves an elongated wire brush strip having bristles that normally extend above the pig body cylindrical surface. For information relating to the use of a foam pig body for cleaning operations wherein a brush means is included on the body cylindrical surface, reference may be had to U.S. Pat. No. 4,720,884 entitled "Cleaning Pig With Debris Flushing Action" issued Jan. 26, 1988 and U.S. Pat. No. 4,825,498 entitled "Cleaning Pig With Selectable Debris Flushing Action" issued May 2, 1989. Each of these patents are incorporated herein by reference.
The two United States patents above-referenced provide cleaning pigs that have produced good results in industrial application. One slight problem encountered with pigs that have wire brushes as a part of the cleaning action is that the wire brushes can, in some applications, scratch the interior surface of the pipeline in which they are used. This is particularly true when the pipeline is made of plastic, or if the pipeline has some other kind of lining that can be marred by metal bristles.
The present invention provides an improved pig for use in cleaning the interior wall of a pipeline. The invention employs an elongated cylindrical pig body made of foam plastic material and includes on the pig body exterior surface, elongated cleaning members positioned in channels. Each cleaning member is made in the form of a strip having a plastic substratum of a width less than the width of channel in which it is positioned. The cleaning member has integral upstanding studs projecting from the substratum, the top surface of the studs forming contact surfaces that engage the interior of a pipe through which the cleaning pig is moved to clean the surface of the pipe without marring or otherwise damaging the surface.